The present invention relates to a catalyst for producing phthalic anhydride and a process for producing it by using the same and, in detail, it relates to a catalyst for producing phthalic anhydride by vapor phase catalytic oxidation of o-xylene and/or naphthalene with molecular oxygen or gas containing molecular oxygen and, to a process for producing phthalic anhydride by using the catalyst.
In recent years, when phthalic anhydride is produced by vapor phase catalytic oxidation of o-xylene and/or naphthalene with molecular oxygen or gas containing molecular oxygen, an increase in the yield is attempted, after obtaining a crude product at first, by treating it with heat and subjecting it to distillation. Since this process is simple and facile to perform, there can be expected a significant effect such that a product of high quality is produced in a large scale with a cheap price.
Furthermore, as a means to elevate the yield, there is a process comprising stabilized production resulting from maintaining reaction conditions and catalytic activity. An example of this process is an oxidation reaction carried out under high load reaction conditions such as high concentration of a starting material gas. However, production of phthalic anhydride from o-xylene or naphthalene is accompanied by violent heat generation and, under high concentration conditions, temperature rise at a hot spot part is extreme, so that excessive oxidation occurs, the yield of phthalic anhydride is lowered, and deterioration of the catalyst is extremely accelerated. Catalysts capable of withstanding such high load reaction conditions have been already proposed, for example, in U.S. Pat. No. 4,356,112.
A widely known catalyst of this kind is a catalyst for producing phthalic anhydride, having supported on an inactive carrier a catalytic active substance containing vanadium oxide and titanium oxide as main components. Catalysts of the type are disclosed, for example, in G.B. 1,203,321, U.S. Pat. No. 4,046,780, Japanese Examined Patent Publication of showa 49-41036, U.S. Pat. No. 3,843,552, U.S. Pat. No. 3,909,457, and Japanese Unexamined Patent Publication of showa 57-105241. These catalysts have their respective features and some of them have been proved as useful by being applied for an industrial use.
There is, however, ample room for improvement of catalyst performance; an increase in yield of only 1% is notable in its economic effect considering the scale of production.